U.S. patent application Ser. No. 099,953, entitled "System for High Resolution Exposure Address With Coarser Resolution Exposing Array", filed Sept. 23, 1987, by Agnostinelli and Mir, describes advantageous imaging devices wherein an object source array (e.g. comprising a linear array of light valve elements) of relatively coarse resolution is imaged at a print zone in a manner providing a relatively higher resolution exposure. In one preferred embodiment, this approach utilizes (i) an object array having exposing pixels of width (w) located with intervening non-exposing spaces so as to have a center-to-center spacing S and (ii) a scan multiplexing optical system, e.g. including lens means and a mirror, which indexes the image of the exposing array in a number of increments, approximately S.div.W, to successive positions across a linear print zone. This system offers important advantages in simplifying array fabrication and in reducing electronic complexities.
One preferred embodiment of the above-described application provides different color filter elements (e.g., red, green and blue filters) repeating series over the exposing pixels sources. Because each pixel source exposes a band at the image zone, it is particularly important that the transmission of the common color sources be equal. Otherwise the boundary between the scan of two adjacent same-color source is visually discernible.
As described in U.S. Pat. No. 4,371,892, the transmission of a crossed-polarizer/PLZT sandwich light valve device with respect to a particular wavelength (color) light is most uniform when operating at the voltage of maximum transmission for that wavelength, which voltage has been termed the .lambda./2 or half-wave voltage. However, different light colors have different half-wave voltages in regard to their transmission through identical light gates of such arrays. To attain uniformity for multicolor printing with such arrays, the '892 patent teaches the application of different voltages, e.g. in a time-multiplexed fashion, for different light color printing actuations. Howver, in the approach of the above-cited application there is no requirement for time-multiplexing the activations of different color exposures. Moreover, it is most convenient to drive adjacent modulators from the same electronic chip having integrated high-voltage drivers providing a single voltage level. Thus the approaches described in the '892 patent have disadvantages when applied to systems such as described in the above-cited application.